1. INTRODUCTION

The general topic of galaxy evolution is enjoying widespread attention
in the literature. The aim is to answer, through observations and
numerical modelling, how galaxies have evolved from the earliest stages
of the Universe, or from a subsequent epoch of formation, to the shape
in which we observe them in the local Universe. The two main strands in
this wide topic are cosmological evolution of galaxies, which deals with
their formation and early evolution, and secular evolution, with which
we mean the internal evolution of galaxies, under the influence of the
dynamical actions of, e.g., bars or spiral arms. Secular evolution, as
comprehensively reviewed by
Kormendy & Kennicutt
(2004),
is a relatively slow process compared to the more rapid evolution undergone
by galaxies in the early Universe, the latter often due to mergers and
galaxy-galaxy interactions.

Because the early stages of galaxy formation and evolution are hard or
sometimes impossible to observe due to the combined effects of distance,
redshift, and dust extinction, the detailed study of nearby galaxies is
one of the very few ways to confirm the detailed predictions of models
of large-scale galaxy formation and evolution. This kind of study can be
nicknamed `galactic palaeontology', because in local galaxies we study
the `fossil record' of billions of years of galaxy evolution - both
cosmological and secular. To read and interpret this fossil record, a
combination of many different observational and interpretational
techniques must be used, from observations of individual stars in our
own Milky Way and the most nearby galaxies to photometric and kinematic
observations across many different wavelengths in external galaxies, all
combined with a wide range of interpretational, analytical and numerical
tools.

Galactic interactions are rare, occurring in only about 2% of local
galaxies (up to 4% if merely bright galaxies are considered;
Knapen & James 2009).
Close companions to local galaxies are much more common, and
Knapen & James (2009)
found that some 15% of local
galaxies have a companion not more than 3 mag fainter than itself
within a radius of five times the diameter of the galaxy under
consideration, and within a range of
± 200 km s-1 in systemic velocity. The
effects on the star formation rate in galaxies of the presence of a
close companion, and even of interactions, is, perhaps surprisingly,
limited (observations by
Bushouse 1987;
Smith et al. 2007;
Woods & Geller 2007;
Li et al. 2008;
Knapen & James 2009;
Jogee et al. 2009;
Rogers et al. 2009;
Ellison et al. 2010,
corroborated by numerical simulations by
Mihos & Hernquist
1996;
Kapferer et al. 2005;
Di Matteo et al. 2007,
2008;
Cox et al. 2008).
Statistically, the star formation rate is raised by a factor of just
under two by the presence of a close companion, but the
H
equivalent width is hardly increased at all
(Knapen & James 2009).
This implies that even
though galaxies with close companions tend to form stars at a higher
rate, they do so over extended periods of time, and not as a burst. Even
the majority of the truly interacting galaxies in
Knapen & James's
(2009)
sample have unremarkable star formation properties. The reason
that extreme star-forming galaxies, such as ultra-luminous infrared
galaxies (ULIRGs) are found to be almost ubiquitously interacting must
surely be a selection effect. In general, interactions do not always
cause starbursts, and starbursts do not always occur in interacting
galaxies.

In fact,
Knapen & James
(2009)
used their sample of 327 nearby disk
galaxies to explore how one might best define the term `starburst'. They
concluded that none of the definitions that are in common use in
the literature can be considered to be objective and generally
discriminant. For instance, selecting galaxies on the basis of their
high star formation rate yields large star-forming disk
galaxies. Selecting those with high equivalent widths (apparently a
bona fide starburst discriminator as this selects galaxies with a
much enhanced current star formation rate as compared to the average
rate in the past), yields primarily late-type galaxies of very small
mass, whose star formation activity is caused by one or a few H II
regions (and which will have
very low impact on the intergalactic medium through, e.g., stellar
winds). And selecting galaxies with the shortest gas depletion
timescales does not only select galaxies with very high current star
formation rates, but also gas-poor early-type galaxies with a very small
star formation rate. The conclusion of
Knapen & James (2009)
is that starbursts are very hard to define properly, and the use of the
term should be restricted to well-described small numbers of objects.

This review deals with aspects of secular evolution, and how we can
trace its actions back through the detailed study of structural
components, particularly bars and rings, in nearby galaxies. The
interpret the effects of these agents, the tools we will use here are
primarily optical and infrared imaging and two-dimensional kinematic
mapping. Other authors have presented reviews on galactic evolution, and
in particular the paper by
Kormendy & Kennicutt
(2004)
presents an
authoritative review of the subject of secular evolution. We will
supplement that by presenting selected recent results on bars and rings
that highlight the intricate and detailed connections that exist between
the different structural components of a galaxy and the overall galactic
evolution.

In Section 2 of this paper, we will review
how the strength of a bar is connected to many of the basic properties
of the bar, such as its length, or the shape of its dust lanes. We will
also see that bars are indeed connected to spirals, and how bars in S0
galaxies may be different from those in spirals.
Section 3 describes how the basic physical
properties of the
host galaxy and, where present, its bar condition the location and
morphology of a nuclear ring, thus highlighting the close physical
connections between these components.
Section 4 discusses how the Spitzer
Survey of Stellar Structure in Galaxies (S4G;
Sheth et al. 2010)
will deliver the data which should allow us to make significant further
progress in
the study of galaxy evolution by means of detailed analyses of the
stellar component in a large sample of nearby galaxies. We briefly
present our conclusions in Section 5.